It is most economical to operate high speed presses continuously because downtime not only increases labor and other operating costs but it also can increase the chances of producing unusable printed material. While press manufacturers have eliminated one possible source of downtime by providing means for insuring a continuous supply of paper to be printed, downtime can still result because of the need to stop the press to remove accumulated printed work.
One approach to handling the output of printed work from a press is to provide a printed work receiving station at the outlet of the press which includes motorized means for both raising an empty pallet to the outlet of the press to receive printed work and lowering a fully loaded pallet for removal. This approach has many advantages and it works well for smaller runs. However on long runs, it is still necessary that the press be shut down when a pallet becomes fully loaded so that it can be replaced with an empty pallet.
An apparatus which enables long printing runs without shutting down the printing press includes a thin piece of plywood that is received between two horizontal support tracks, the tracks being pivotally positioned at the outlet of the printing press above and parallel to the top of a loaded pallet. Once a pallet is fully loaded, without turning off the printing press, the sheet of plywood is inserted between the two support tracks in a horizontal printed work receiving position permitting printed work to be collected on the sheet of plywood. After insertion of the plywood sheet the loaded pallet is lowered and replaced with an empty pallet. The empty pallet then can be raised up into a receiving position for the printed work directly under the plywood sheet. The support tracks are pivotally moved out of the their supporting position along the edges of the plywood sheet allowing the plywood sheet and the collected printed work thereon to fall onto the empty pallet. New printed work exiting from the outlet of the press then accumulates on the new pallet.
Although an apparatus of the above kind enables long printing runs without the need to turn off the press, the large quantities of plywood necessary for long runs can be very expensive. Each time a plywood sheet is inserted into the receiving area, because of the friction between the plywood and the accumulated printed work thereon, the plywood must remain underneath the printed work and cannot be easily removed until the printed work is taken off the sheet. In many instances, printed work will remain on a loaded pallet for days and even weeks at a time, thus rendering the plywood sheet between the printed work and the pallet unusable for a second pallet exchange.
Long printing runs that do not use plywood have been accomplished by employing a large metallic multi-pronged fork like apparatus (fork) that is inserted above a loaded pallet in place of the plywood. Utilizing this apparatus, after a full pallet is replaced with an empty pallet, and the empty pallet is raised up below the fork, the fork is removed from under the printed work collected thereon to permit that printed work and additional printed work exiting the press outlet to collect upon the top of the previously empty pallet. The fork, instead of being supported by support tracks that outwardly pivot, is supported on its peripheral edges by linear bearings that are supposed to allow the fork to be inserted and removed easily. Using a multi-pronged fork instead of a full plywood sheet, the actual surface area of the temporary printed work collector that frictionally contacts the printed works is minimized and therefore, removal of the collector, without the printed work following, is facilitated.
One problem with the fork apparatus is that many printed works may exit the printing press with a certain degree of curl or bow in them. When the fork like apparatus is inserted, printed work having curl or bow many times may come off the press under some of the fork prongs and on top of others, in effect woven between the prongs of the fork. When a printed work is woven under even a single fork prong, the friction between the prong and the printed work increases substantially. Upon removal of the fork, interwoven printed works follow the apparatus out of, or partially out of, the printed work receiving station and many times are destroyed or rendered unusable.
Another problem with the fork apparatus is that the linear bearings that support the apparatus quickly wear out. Worn linear bearings either have to be replaced or the fork operator must struggle to insert and remove the fork apparatus.
It would be advantageous to have an improved durable work receiving station that would permit a full pallet to be replaced by an empty pallet without shutting down the press and without destroying any of the printed works.